1. Technical Field
This invention relates to a method of splicing optical fibers, and optical fibers spliced thereby.
2. Description of the Prior Art
Various methods have been developed for connecting two optical fibers. Connectors and splices are two general categories of optical fiber joining techniques. While connectors typically have the ability to make multiple connects and disconnects, splices are usually used when lowest loss is desired in connecting two optical fibers. Currently, there are two general categories of optical fiber splices: fusion splices and cement splices. In fusion splices, the ends of two optical fibers are brought together, and the fiber is melted by a flame or electric arc, etc., in order to join the ends. In cement splices, the optical fiber ends are brought together and joined by means of a cement.
The low loss and wide bandwidth of single mode optical fibers promise excellent high capacity long distance communications. However, the small core diameter (typically less than 15 micrometers) of single mode fibers makes splicing more difficult than with multimode fibers, and the effects of end quality and transverse and angular misalignment are more critical. Reports of fiber losses as low as 0.35 db/km at 1.3 .mu.m, and even less at 1.55 .mu.m, make low loss splicing techniques important for maximum repeater spacing. For example, if a splice is placed, on average, every kilometer in a fiber that has an inherent loss of 0.4 db/km, and if the splice itself adds an additional 0.2 db loss, the average loss of the spliced fiber will be 0.6 db/km. However, if the splice loss is reduced to 0.1 db, the average loss of the spliced fiber would be 0.5 db/km. For a typical single mode optical fiber system, this reduction in loss is estimated to yield an increase in maximum repeater spacing of about 1 to 2 kilometers. Thus, a very significant economic benefit is realized by reducing the splice loss between low loss fibers.
Conventional splicing techniques that rely on the alignment of the outer diameter of the fiber, such as "V" grooves, rods, tubes, and to some extent arc and flame fusion, achieve lowest splice losses only for fibers with well-centered (&lt;0.2 .mu.m eccentricity) cores. Submicron core centering tolerances probably cannot be maintained in large-scale manufacturing; therefore, splicing of nonidentical fibers relying on cladding alignment methods can expect higher losses. This includes arc and flame fusion which have outside diameter or cladding self-aligning effects due to surface tension.